Laminate substrate, freestanding substrate, method for manufacturing laminate substrate, and method for manufacturing freestanding substrate

ABSTRACT

A laminate substrate which includes a single crystal diamond (111) layer, including: an underlying substrate, an intermediate layer on the underlying substrate, and the single crystal diamond (111) layer on the intermediate layer, in which the underlying substrate has a main surface which has an off angle within a range, −8.0° or more and −0.5° or less, or +0.5° or more and +8.0° or less in a crystal axis [_1_1 2] direction or a threefold symmetry direction thereof relative to a crystal plane orientation of (111), and the single crystal diamond (111) layer has an off angle within a range, more than −10.5° and less than −2.0°, or more than +2.0° and less than +10.5° in the crystal axis [_1_1 2] direction or a threefold symmetry direction thereof relative to the crystal plane orientation of (111).

TECHNICAL FIELD

The present invention relates to a laminate substrate which has a singlecrystal diamond (111), a freestanding substrate, a method formanufacturing a laminate substrate and a method for manufacturing afreestanding substrate.

BACKGROUND ART

Diamond has a wide band gap of 5.47 eV at room temperature, and is knownas a wide bandgap semiconductor.

Among semiconductors, diamond has extremely high dielectric breakdownelectric field strength of 10 MV/cm, and a high-voltage operation can beperformed. In addition, diamond has the highest thermal conductivityamong known materials, and has an excellent heat radiation propertythereby. Further, diamond has very large carrier mobility and saturateddrift velocity, and is suitable for a high speed device.

Accordingly, diamond has the highest Johnson performance index, whichindicates a property as a radio-frequency and high power device,compared to semiconductors such as silicon carbide and gallium nitride,and is said to be an ultimate semiconductor thereby.

Further, diamond has a phenomenon of nitrogen-vacancy center (NVC)within the crystal, and can manipulate and detect a single spin in roomtemperature, and has the characteristic that the condition can be imagedby photo detection magnetic resonance. Making use of thischaracteristic, application in a wide field of high-sensitivity sensorsfor magnetic field, electric field, temperature, and pressure, etc. isexpected.

CITATION LIST Non Patent Literature

-   Non Patent Document 1: M. Hatano et al., OYOBUTURI 85, 311 (2016)

PATENT LITERATURE

-   Patent Document 1: US Unexamined Patent publication No.    US2013/0143022A1

SUMMARY OF INVENTION Technical Problem

As described above, diamond is expected to be used practically asmaterial for semiconductors or material for electronic and magneticdevices, and supply of a diamond substrate with a large area and highquality is desired. In particular, for use in a NVC device of highimportance, the NV axis has to be highly oriented, and therefore, thediamond surface is preferably a (111) crystal surface with the NV axisaligned in a [111]direction (Non Patent Document 1). In addition, forexample, considering application in an MRI field for medical purposes, adevice that can measure a wider range efficiently can be realized with adiamond substrate that has a large diameter as the magnetic sensorportion. In addition, there is an advantage considering manufacturingcosts.

However, currently, a diamond (111) crystal with a large area and highquality cannot be obtained. Presently, Ib type and IIa type diamondsynthesized by a High Pressure and High Temperature (HPHT) method areknown for use as a diamond substrate, but the Ib type diamond containsmany nitrogen impurities. The IIa type diamond has a comparativelylowered amount of nitrogen impurities as volume average, but there isconsiderable non-uniformity depending on the part of the crystal. Inaddition, practicality is not high since diamond with a (111) surface isonly obtained in sizes of up to about 8 mm diameter at most.

In Patent Document 1, a technology to form a diamond (111) crystal byheteroepitaxial growth using a chemical vapor deposition (CVD) method isreported. However, it is unclear whether the size and characteristics ofthe resulting diamond (111) crystal are on a sufficient level. Inaddition, including the technology described in Patent Document 1, thereis no other information of being put to practical use.

The present invention was accomplished in order to solve the aboveproblems, and it is an object of the present invention to provide alaminate substrate with a high-quality single crystal diamond (111) thathas a large area (large diameter), high crystallinity, few hillocks,abnormal growth particles, and dislocation defects etc., high purity andlow stress, applicable in electronic and magnetic devices, alarge-diameter freestanding single crystal diamond (111) substrate, amethod for manufacturing the laminate substrate, and a method formanufacturing the freestanding substrate.

Solution to Problem

The present invention was accomplished in order to achieve the aboveobject and provides a laminate substrate which includes a single crystaldiamond (111) layer, comprising: an underlying substrate, anintermediate layer on the underlying substrate, and the single crystaldiamond (111) layer on the intermediate layer, wherein the underlyingsubstrate has a main surface which has an off angle within a range,−8.0° or more and −0.5° or less, or +0.5° or more and +8.0° or less in acrystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to a crystal plane orientation of (111), and the singlecrystal diamond (111) layer has an off angle within a range, more than−10.5° and less than −2.0°, or more than +2.0° and less than +10.5° inthe crystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to the crystal plane orientation of (111).

Such a laminate substrate will have a high-quality single crystaldiamond (111) layer that has a large diameter, high crystallinity, fewhillocks, abnormal growth particles, and dislocation defects etc., highpurity and low stress, suitable for electronic and magnetic devices.

At this time, the intermediate layer of the laminate substrate may havean outermost surface which is a metal film selected from an Ir (111)film, a Rh (111) film, a Pd (111) film, and a Pt (111) film.

At this time, the underlying substrate of the laminate substrate may bea substrate consisting of a single Si, MgO, Al₂O₃, SiO₂, Si₃N₄, or SiC,or a laminated body selected from Si, MgO, Al₂O₃, SiO₂, Si₃N₄, or SiC.

This allows a laminate substrate with low manufacturing costs.

At this time, the underlying substrate of the laminate substrate may beMgO (111) or a MgO (111) layer may be further comprised between theunderlying substrate and the intermediate layer.

This allows a laminate substrate which has a single crystal diamond(111) layer of higher quality.

At this time, the outermost surface of the intermediate layer of thelaminate substrate may be a heteroepitaxially grown Ir (111) film, andthe Ir (111) film may have a crystallinity wherein a half band width(FWHM) of a diffracted intensity peak at 2θ=40.7° assigned to Ir (111)analyzed by an X-ray diffraction method with a wavelength of λ=1.54 Å is0.30° or less.

This allows a laminate substrate which has a single crystal diamond(111) layer of higher crystallinity.

At this time, the intermediate layer of the laminate substrate may havea thickness of 5.0 μm or less.

This reduces stress, and reduces concern for the occurrence of warps orcracks.

At this time, a surface of the metal film of the outermost surface ofthe intermediate layer of the laminate substrate, which is afilm-forming surface of the single crystal diamond (111) layer may havean off angle within a range, −8.0° or more and −0.5° or less, or +0.5°or more and +8.0° or less in a crystal axis [_1_1 2] direction or athreefold symmetry direction thereof relative to a crystal planeorientation of (111)

In this way, the single crystal diamond (111) layer will have evenhigher crystallinity.

At this time, the single crystal diamond (111) layer of the laminatesubstrate may have a crystallinity wherein a half band width (FWHM) of adiffracted intensity peak at 2θ=43.9° assigned to diamond (111) analyzedby an X-ray diffraction method with a wavelength of λ=1.54 Å is 1° orless, and an FWHM of a rocking curve peak is 4° or less.

In this way, the laminate substrate will have higher quality and will bemore suitable as a substrate for electronic and magnetic devices.

At this time, the single crystal diamond (111) layer of the laminatesubstrate may have, out of impurity concentrations analyzed by SIMSmethod, an oxygen concentration of 1×10¹⁷ atoms/cm³ or less and anitrogen concentration of 5×10¹⁶ atoms/cm³ or less.

In this way, the laminate substrate becomes more suitable as a substratefor electronic and magnetic devices.

At this time, the single crystal diamond (111) layer of the laminatesubstrate may have a thickness of 100 μm or more.

In this way, the single crystal diamond (111) layer will have higherstrength, and will easily become a freestanding substrate, removing theunderlying substrate and the intermediate layer.

At this time, the laminate substrate may have a diameter of 10 mm ormore.

This allows the formation of many elements on one chip, reduction ofcosts, and miniaturization of measuring devices.

At this time, the single crystal diamond (111) layer of the laminatesubstrate may have a surface whose arithmetic average roughness (Ra) is2 nm or less.

Such a laminate substrate allows easy formation of elements, and is moresuitable as a substrate for electronic and magnetic devices.

The present invention further provides a freestanding single crystaldiamond (111) substrate, wherein the freestanding substrate has a mainsurface which has an off angle within a range, more than −10.5° and lessthan −2.0°, or more than +2.0° and less than +10.5° in a crystal axis[_1_1 2] direction or a threefold symmetry direction thereof relative toa crystal plane orientation of (111), and the freestanding substrate hasa thickness of 100 μm or more.

This allows a high-quality freestanding single crystal diamond (111)substrate that has a large diameter, high crystallinity, few hillocks,abnormal growth particles, and dislocation defects etc., high purity andlow stress, suitable for electronic and magnetic devices with a widerange of application such as high-sensitivity sensors of magnetic field,electric field, temperature, and pressure.

The present invention further provides a method for manufacturing alaminate substrate which includes a single crystal diamond (111) layer,comprising: a step of heteroepitaxially growing an intermediate layer onan underlying substrate whose main surface has an off angle within arange, −8.0° or more and −0.5° or less, or +0.5° or more and +8.0° orless in a crystal axis [_1_1 2] direction or a threefold symmetrydirection thereof relative to a crystal plane orientation of (111), anuclei formation step of forming diamond nuclei on a surface of theintermediate layer, and a step of heteroepitaxially growing, on theintermediate layer surface on which the nuclei are formed, a singlecrystal diamond (111) layer which has an off angle within a range, morethan −10.5° and less than −2.0°, or more than +2.0° and less than +10.5°in a crystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to a crystal plane orientation of (111).

In this way, a laminate substrate with a high-quality single crystaldiamond (111) layer that has a large diameter, high crystallinity, fewhillocks, abnormal growth particles, and dislocation defects etc., highpurity and low stress, suitable for electronic and magnetic devices isprovided.

At this time, in the step of heteroepitaxially growing the intermediatelayer, the intermediate layer may be a metal film selected from an Ir(111) film, a Rh (111) film, a Pd (111) film, and a Pt (111) film.

At this time, in the step of heteroepitaxially growing the singlecrystal diamond (111) layer, the diamond layer which isheteroepitaxially grown may have a thickness of 100 μm or more.

In this way, a laminate substrate that has a single crystal diamond(111) layer with higher strength can be manufactured.

At this time, in the step of heteroepitaxially growing the intermediatelayer, a substrate which is MgO (111) crystal at least on an outermostsurface may be used as the underlying substrate, and in the step ofheteroepitaxially growing the intermediate layer, the intermediate layermay be heteroepitaxially grown by an R. F. magnetron sputtering methodunder conditions: a substrate temperature of 60° to 1200° C. and apressure of 1.1×10⁻¹ Torr (14.7 Pa) to 9.0×10⁻¹ Torr (120.0 Pa)

In this way, a laminate substrate which has a single crystal diamond(111) layer of higher quality can be manufactured.

At this time, a freestanding single crystal diamond (111) substrate maybe obtained by removing at least the intermediate layer and theunderlying substrate from the laminate substrate obtained by the abovemethod for manufacturing a laminate substrate.

In this way, a high-quality freestanding single crystal diamond (111)substrate that has a large diameter, high crystallinity, few hillocks,abnormal growth particles, and dislocation defects etc., high purity andlow stress, suitable for electronic and magnetic devices with a widerange of application such as high-sensitivity sensors of magnetic field,electric field, temperature, and pressure can be provided.

Advantageous Effects of Invention

As described above, the inventive laminate substrate has a high-qualitysingle crystal diamond (111) layer that has a large diameter, highcrystallinity, few hillocks, abnormal growth particles, and dislocationdefects etc., high purity and low stress, suitable for electronic andmagnetic devices. The inventive freestanding substrate has ahigh-quality single crystal diamond (111) layer that has a largediameter, high crystallinity, few hillocks, abnormal growth particles,and dislocation defects etc., high purity and low stress, suitable forelectronic and magnetic devices. In addition, the inventive method formanufacturing a laminate substrate can provide a method formanufacturing a laminate substrate that has a high-quality singlecrystal diamond (111) layer with a large diameter, high crystallinity,few hillocks, abnormal growth particles, and dislocation defects etc.,high purity and low stress, suitable for electronic and magneticdevices.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing which explains plane orientation;

FIG. 2 shows an example of the inventive laminate substrate;

FIG. 3 shows an example of the inventive freestanding substrate.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail, but thepresent invention is not limited thereto.

As described above, obtention of a high quality single crystal diamond(111) layer that has a large diameter, high crystallinity, few hillocks,abnormal growth particles, and dislocation defects etc., high purity andlow stress, suitable for electronic and magnetic devices has beenrequired.

The present inventor has diligently investigated the above problems, andas a result, has found that a laminate substrate which includes a singlecrystal diamond (111) layer, comprising: an underlying substrate, anintermediate layer on the underlying substrate, and the single crystaldiamond (111) layer on the intermediate layer, wherein the underlyingsubstrate has a main surface which has an off angle within a range,−8.0° or more and −0.5° or less, or +0.5° or more and +8.0° or less in acrystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to a crystal plane orientation of (111), and the singlecrystal diamond (111) layer has an off angle within a range, more than−10.5° and less than −2.0°, or more than +2.0° and less than +10.5° inthe crystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to the crystal plane orientation of (111) was alaminate substrate which has a high quality single crystal diamond (111)layer that has a large diameter, high crystallinity, few hillocks,abnormal growth particles, and dislocation defects etc., high purity andlow stress, suitable for electronic and magnetic devices, and completedthe present invention.

In addition, the present inventor has found that a freestanding singlecrystal diamond (111) substrate, wherein the freestanding substrate hasa main surface which has an off angle within a range, more than −10.5°and less than −2.0°, or more than +2.0° and less than +10.5° in acrystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to a crystal plane orientation of (111), and thefreestanding substrate has a thickness of 100 μm or more was a highquality freestanding single crystal diamond (111) substrate that has alarge diameter, high crystallinity, few hillocks, abnormal growthparticles, and dislocation defects etc., high purity and low stress,suitable for electronic and magnetic devices, and completed the presentinvention.

In addition, the present inventor has found that a laminate substratewhich has a high quality single crystal diamond (111) layer that has alarge diameter, high crystallinity, few hillocks, abnormal growthparticles, and dislocation defects etc., high purity and low stress,suitable for electronic and magnetic devices can be obtained by a methodfor manufacturing a laminate substrate which includes a single crystaldiamond (111) layer, comprising: a step of heteroepitaxially growing anintermediate layer on an underlying substrate whose main surface has anoff angle within a range, −8.0° or more and −0.5° or less, or +0.5° ormore and +8.0° or less in a crystal axis [_1_1 2] direction or athreefold symmetry direction thereof relative to a crystal planeorientation of (111), a nuclei formation step of forming diamond nucleion a surface of the intermediate layer, and a step of heteroepitaxiallygrowing, on the intermediate layer surface on which the nuclei areformed, a single crystal diamond (111) layer which has an off anglewithin a range, more than −10.5° and less than −2.0°, or more than +2.0°and less than +10.5° in a crystal axis [_1_1 2] direction or a threefoldsymmetry direction thereof relative to a crystal plane orientation of(111), and completed the present invention.

Hereinafter, the present invention will be described with reference todrawings.

Firstly, terms used in the present description will be defined.

In the present description, a crystal layer and a crystal film whosemain surfaces are (111) surfaces will be called simply “(111) layer” and“(111) film”. For example, a single crystal diamond layer whose mainsurface is a (111) surface will be called “single crystal diamond (111)layer”.

The idea of off angles is shown in FIG. 1. FIG. 1 shows a conceptualdiagram of the [_1_1 2] direction and the threefold symmetry directionsthereof, [_1 2_1] and [2_1_1] directions and the off angle of asubstrate whose main surface is a (111) surface. Incidentally, in thepresent description,

a [1 1 2] direction will be written as a [_1_1 2] direction.

(Laminate Substrate)

A laminate substrate 100 of the present invention includes an underlyingsubstrate 1, an intermediate layer 2 on the underlying substrate 1, andthe single crystal diamond (111) layer 3 on the intermediate layer 2 asshown in FIG. 2. In FIG. 2, the underlying substrate 1 and theintermediate layer 2 are described as having one layer each, but theymay have several layers each.

The underlying substrate 1 has a main surface which has an off anglewithin the range, −8.0° or more and −0.5° or less, or +0.5° or more and+8.0° or less in a crystal axis [_1_1 2] direction or a threefoldsymmetry direction thereof relative to a crystal plane orientation of(111). When the off angle is within such a range, growth progresses inthe direction of the step of the single crystal diamond (111) crystal(crystal axis [_1_1 2] direction and the threefold symmetry directionsthereof), and a favorable crystal can be obtained. If the off angle iswithin the range, more than −0.5° and less than +0.5°, growth in thedirection of the step as described above cannot be easily performed, anda favorable crystal cannot be obtained. In addition, if the off angle iswithin the range, less than −8.0° and the range, more than +8.0°,growing for a long time causes polycrystallization, and a single crystalof good quality cannot be obtained.

The underlying substrate 1 is preferably a substrate consisting of asingle Si, MgO, Al₂O₃, SiO₂, Si₃N₄, or SiC, or a laminated body selectedfrom Si, MgO, Al₂O₃, SiO₂, Si₃N₄, or SiC. With these materials, it iseasy to set the crystal plane orientation (including the off angle) ofthe main surface of the underlying substrate 1. The materials are alsorelatively cheap and can be acquired easily.

The underlying substrate 1 is preferably MgO (111) or a MgO (111) layeris further comprised between the underlying substrate 1 and theintermediate layer 2. An intermediate layer 2 and a single crystaldiamond (111) layer 3 can be formed on the MgO (111).

The intermediate layer 2 may be one layer or a laminated body of severallayers. An outermost surface of the intermediate layer 2 is preferably ametal film selected from an Ir (111) film, a Rh (111) film, a Pd (111)film, and a Pt (111) film. When such a metal film is used, diamondnuclei tend to have high density when a nucleation treatment (biastreatment) is performed, and this is favorable since the single crystaldiamond (111) layer 3 is more easily formed thereon.

The intermediate layer 2 is more preferably a heteroepitaxially grown Ir(111) film. At this time, the single crystal diamond (111) layer 3 willhave higher crystallinity if the Ir (111) film has a crystallinity inwhich a half band width (FWHM) of a diffracted intensity peak at2θ=40.7° assigned to Ir (111) analyzed by an X-ray diffraction methodwith a wavelength of λ=1.54 Å is 0.30° or less.

The intermediate layer 2 preferably has an off angle within the range,±0.5 to ±8.0° in a crystal axis [_1_1 2] direction or a threefoldsymmetry direction thereof relative to a crystal plane orientation of(111) With such an off angle, growth is more inclined to progress in thedirection of the step of the single crystal diamond (111) layer 3 ([_1_12] direction and the threefold symmetry directions thereof), and afavorable crystal growth can be obtained. That is, the single crystaldiamond (111) layer 3 becomes smooth, with no abnormal growth.

The thickness of the intermediate layer 2 is preferably 5.0 μm or less.With such a range, the stress becomes smaller, and there is less concernfor the occurrence of warps or cracks.

As favorable examples of the underlying substrate 1 and the intermediatelayer 2, for example, a MgO (111) substrate may be used as theunderlying substrate 1 and an Ir (111) film may be heteroepitaxiallygrown on the MgO (111) substrate, or a Si (111) substrate may be used asthe underlying substrate 1, and after heteroepitaxially growing a MgO(111) layer on the Si (111) substrate, an Ir (111) film may further beheteroepitaxially grown.

The single crystal diamond (111) layer 3 has an off angle within arange, more than −10.5° and less than −2.0°, or more than +2.0° and lessthan +10.5° in the crystal axis [_1_1 2] direction or a threefoldsymmetry direction thereof relative to the crystal plane orientation of(111). As a result of diligent research, the present inventor has foundthat the off angle of the single crystal diamond (111) layer 3 is largerthan the off angle of the underlying substrate 1 by more than 1.5° andless than 2.5°. For this reason, the off angle of the single crystaldiamond (111) layer 3 which is heteroepitaxially grown on the underlyingsubstrate 1 that has an off angle as described above becomes larger thanthe off angle of the underlying substrate 1 by more than 1.5° and lessthan 2.5°. Conversely, an underlying substrate 1 which has an off anglewithin a range that allows obtention of a good quality film and has anoff angle that is smaller than the target off angle of the singlecrystal diamond (111) layer 3 by more than 1.5° and less than 2.5° maybe used.

The off angle of the single crystal diamond (111) layer 3 is morepreferably within the range, −8.0° or more and −3.0° or less, or +3.0°or more and +8.0° or less in the crystal axis [_1_1 2] direction or athreefold symmetry direction thereof. A single crystal diamond (111)layer 3 which has an off angle of such a range is of higher quality, andis more suitable as a substrate for electronic and magnetic devices.

The impurity concentration of the single crystal diamond (111) layer 3is preferably: an oxygen concentration of 1×10¹⁷ atoms/cm³ or less and anitrogen concentration of 5×10¹⁶ atoms/cm³ or less when analyzed by SIMSmethod. Such impurity concentration is suitable for a substrate forelectronic and magnetic devices.

The thickness of the single crystal diamond (111) layer 3 is preferably100 μm or more. A single crystal diamond (111) layer 3 with such athickness has higher strength, and can easily become a freestandingsubstrate 4 as in FIG. 3, removing the underlying substrate 1 and theintermediate layer 2.

The diameter of the laminate substrate 100 is preferably 10 mm or more.Such a substrate with a large diameter, that is, a large area, allowsthe formation of many elements on one chip, reduction of costs, andminiaturization of measuring devices.

The arithmetic average roughness (Ra) of the surface of the singlecrystal diamond (111) layer 3 is preferably 2 nm or less. A laminatesubstrate 100 provided with a single crystal diamond (111) layer 3 whichhas such a surface arithmetic average roughness (Ra) allows easyformation of elements, and is suitable as a substrate for electronic andmagnetic devices.

(Freestanding Substrate)

As stated above, a freestanding substrate 4 can be obtained by removingthe underlying substrate 1 and the intermediate layer 2 (FIG. 3). With afreestanding substrate 4, which does not have an underlying substrate 1or an intermediate layer 2, there is no hetero interface, which becomesthe source of noise, and the range of application becomes wider; notonly for use for electronic devices, but also for high-sensitivitysensors of magnetic field, electric field, temperature, pressure, etc.

(Method for Manufacturing a Laminate Substrate)

Next, the inventive method for manufacturing a laminate substrate 100will be described.

Firstly, the above-described underlying substrate 1 is prepared. Next,an intermediate layer 2 is heteroepitaxially grown on the underlyingsubstrate 1. The method of heteroepitaxial growth is not particularlylimited. For example, when the above intermediate layer 2 is a metalfilm, electron beam evaporation method and the sputtering method, etc.are possible. The R. F. magnetron sputtering method is favorable sincethe growth rate is relatively high and a favorable crystallinity can beobtained. Growth conditions can be set appropriately according to thetype of film, but as typical conditions, a substrate temperature of 600to 1200° C. and a pressure of 1.1×10⁻¹ Torr (14.7 Pa) to 9.0×10⁻¹ Torr(120.0 Pa) allows heteroepitaxial growth of a high-quality metal film.

After forming, for example, a metal film as the intermediate layer 2, anucleation treatment is performed in which diamond nuclei are formed onthe surface of the intermediate layer 2. Formation of diamond ispromoted by performing the nucleation treatment. This nucleationtreatment is performed by, for example, biasing the substrate whileperforming a plasma treatment in a gas atmosphere containing carbon.

After forming nuclei on the surface of the intermediate layer 2, asingle crystal diamond (111) layer 3 is heteroepitaxially grown. Achemical vapor deposition method (CVD method) is suitable for thisgrowth, and for example, a microwave plasma CVD method, a direct currentplasma CVD method, a hot-filament CVD method, and an arc dischargeplasma jet CVD method, etc. are possible. A diamond obtained by thesegrowing methods is a high-quality single crystal diamond with highcrystallinity, few hillocks, abnormal growth particles and dislocationdefects, and has high purity and low stress. Among these, the directcurrent plasma CVD method is suitable since it allows swift growth withhigh purity and high crystallinity. In this way, a laminate substrate100 with an underlying substrate 1, an intermediate layer 2, and asingle crystal diamond (111) layer 3 laminated can be manufactured.

When applying the single crystal diamond (111) layer 3 to variousdevices etc., if a thin single crystal diamond (111) layer 3 issufficient, then it may be used as single crystal diamond (111) layer3/intermediate layer 2/underlying substrate 1, in order to hold thesingle crystal diamond (111) layer 3 stably.

(Method for Manufacturing a Freestanding Substrate)

If the existence of the materials of the intermediate layer 2 and belowbecome the cause of noise in using as magnetic sensors etc., the singlecrystal diamond (111) layer 3 alone may be taken out as a freestandingsingle crystal diamond (111) substrate 4. By removing the underlyingsubstrate 1 and the intermediate layer 2 from the laminate substrate 100obtained as described above, a freestanding single crystal diamond (111)substrate 4 can be obtained. The removal of the underlying substrate 1and the intermediate layer 2 is not particularly limited. A mechanicaltreatment such as polishing or a wet or dry etching treatment etc. maybe appropriately selected according to the materials of the underlyingsubstrate 1 and the intermediate layer 2. The above treatments may alsobe combined.

In addition, smoothing the surface of the laminate substrate 100 whichhas the above single crystal diamond (111) layer 3 formed or the abovefreestanding substrate 4 is also effective for application to electronicand magnetic devices etc. This makes the formation of an element easier.For smoothing the surface, mechanical polishing, CMP, or dry etchingsuch as plasma etching etc. are possible.

Example

Hereinafter, the present invention will be described in detail withreference to an Example, but the present invention is not limitedthereto.

Example

As an underlying substrate, a single crystal MgO substrate polished onone side which has a diameter of 20.0 mm, a thickness of 1.0 mm, a mainsurface that is a (111) surface and an off angle of 2° in a crystal axis[_1_1 2] direction (hereinafter referred to as “single crystal MgO (111)substrate”) was prepared.

Next, an intermediate layer of a single crystal Ir film was formed by R.F. magnetron sputtering method on the surface of the prepared singlecrystal MgO (111) substrate. The single crystal Ir film was formed by aradio-frequency (RF) magnetron sputtering method (13.56 MHz) withtargeting at Ir which has a diameter of 6 inches (150 mm), a thicknessof 5.0 mm, and purity of 99.9% or more.

The single crystal MgO (111) substrate, which is an underlying substratewas heated to 800° C., and after it was confirmed that the base pressurehad become 6×10⁻⁷ Torr (about 8.0×10⁻⁵ Pa) or lower, 50 sccm of Ar gaswas introduced. Next, after making the pressure 3×10⁻¹ Torr (about 39.9Pa) by adjusting the aperture of the valve connected to the exhaustsystem, film formation was performed for 15 minutes by inputting RFpower of 1000 W. In this way, a single crystal Ir film with a thicknessof 1.0 μm was obtained.

A single crystal MgO (111) substrate on which a single crystal Ir filmis laminated in the way described above grows heteroepitaxially inaccordance with the off angle of the single crystal MgO substrate. Thissingle crystal Ir film was analyzed by an X-ray diffraction method witha wavelength of λ=1.54 Å, and the surface was a (111) surface and therewas an off angle of 2° in the crystal axis [_1_1 2] direction. Inaddition, the half width (FWHM) of the diffracted peak at 2θ=40.7°,assigned to Ir (111) was 0.187°. Hereinafter, this single crystal Irfilm will be referred to as “Ir (111) film”.

Next, as pre-treatment for forming diamond nuclei, a nucleationtreatment (bias treatment) was performed. The substrate was set on aplanar electrode with a diameter of 25 mm inside a treatment chamberwith the Ir (111) film side facing upwards. After it was confirmed thatthe base pressure had become 1×10⁻⁶ Torr (about 1.3×10⁻⁴ Pa) or lower,hydrogen-diluted methane gas (CH₄/(CH₄+H₂)=5.0 vol. %) was introducedinto the treatment chamber at a flow rate of 500 sccm. After making thepressure 100 Torr (about 1.3×10⁴ Pa) by adjusting the aperture of thevalve connected to the exhaust system, a negative voltage was applied toan electrode at the substrate side to expose to plasma for 90 seconds,and thereby the substrate (Ir (111) film) surface was subjected to biastreatment.

Diamond was heteroepitaxially grown on the Ir (111) film/single crystalMgO (111) substrate produced as described above by a direct currentplasma CVD method. The Ir (111) film/single crystal MgO (111) substratesubjected to bias treatment was set inside the chamber of a directcurrent plasma CVD apparatus, and after exhausting was performed using arotary pump until the base pressure became 10³ Torr (about 1.3×10⁻¹ Pa)or lower, hydrogen-diluted methane gas (CH₄/(CH₄+H₂)=5.0 vol. %) wasintroduced into the chamber as a source gas at a flow rate of 1000 sccm.After making the pressure inside the chamber 110 Torr (about 1.5×10⁴ Pa)by adjusting the aperture of the valve connected to the exhaust system,film formation was performed for 30 hours by sending a direct current of6.0 Å, whereby the film formation was performed until the thicknessreached about 200 μm. The temperature of the substrate during filmformation was measured by a pyrometer, and it was 950° C. In this way, adiamond layer was heteroepitaxially grown on the Ir (111) film/singlecrystal MgO (111) substrate, and a laminate substrate was obtained.

Regarding the obtained diamond layer, X-ray diffraction analysis wasperformed with an incident wavelength of 1.54 Å, and the FWHM of thediffracted intensity peak and the FWHM of the rocking curve peak at2θ=43.9°, assigned to diamond (111) were respectively 0.212° and 0.583°.The diamond layer grew heteroepitaxially in accordance with the offangle of the Ir (111) film. Hereinafter, this diamond layer will bereferred to as “single crystal diamond (111) layer”.

The impurity concentration of the single crystal diamond (111) layer wasanalyzed by SIMS method, and oxygen concentration was [O]≤1×10¹⁷atoms/cm³, and nitrogen concentration was [N]≤5×10¹⁶ atoms/cm³.Incidentally, both elements were below the lower measurement limit ofthe device. In addition, optical microscope and SEM observation wasperformed, and no crystal defects such as hillocks and abnormal growthparticles were found. Even in a single crystal diamond (111) layer/Ir(111) film/single crystal MgO (111) substrate form, there were no cracksor warps.

Subsequently, the Ir (111) film/single crystal MgO (111) substrate wasremoved to make a freestanding substrate. Firstly, after removing thesingle crystal MgO (111) substrate by etching, the Ir (111) film wasremoved by polishing. As a result, a freestanding single crystal diamond(111) substrate with a diameter of 20 mm and a thickness of about 200 μmwas obtained.

Lastly, the surface of the freestanding single crystal diamond (111)substrate was polished. Measuring using a probe type surface roughnesstester (Dektak made by Bruker Corporation) by 500 μm scanning, thearithmetic average roughness (Ra) was 0.5 nm.

Here, a 3 μm thick nitrogen-doped diamond layer was formed on thesurface of the obtained polished freestanding single crystal diamond(111) substrate with a diameter of 20 mm and a thickness of 180 μm by amicrowave CVD method, mixing nitrogen gas with hydrogen-diluted methanesource gas. The nitrogen-doped diamond layer was analyzed by SIMS, andthe nitrogen concentration in the nitrogen-doped diamond layer was[N]=1×10¹⁹ atoms/cm³.

Subsequently, in order to evaluate NVC phenomenon, photoluminescence(PL) analysis, photo detection magnetic resonance analysis, and confocalmicroscope observation of light detected from an NV center wereperformed, and it was confirmed that there was sufficient practicalityfor use in a magnetic sensor device.

It should be noted that the present invention is not limited to theabove-described embodiments. The embodiments are just examples, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept disclosedin claims of the present invention are included in the technical scopeof the present invention.

1. A laminate substrate which includes a single crystal diamond (111)layer, comprising: an underlying substrate, an intermediate layer on theunderlying substrate, and the single crystal diamond (111) layer on theintermediate layer, wherein the underlying substrate has a main surfacewhich has an off angle within a range, −8.0° or more and −0.5° or less,or +0.5° or more and +8.0° or less in a crystal axis [_1_1 2] directionor a threefold symmetry direction thereof relative to a crystal planeorientation of (111), and the single crystal diamond (111) layer has anoff angle within a range, more than −10.5° and less than −2.0°, or morethan +2.0° and less than +10.5° in the crystal axis [_1_1 2] directionor a threefold symmetry direction thereof relative to the crystal planeorientation of (111).
 2. The laminate substrate according to claim 1,wherein the intermediate layer has an outermost surface which is a metalfilm selected from an Ir (111) film, a Rh (111) film, a Pd (111) film,and a Pt (111) film.
 3. The laminate substrate according to claim 1,wherein the underlying substrate is a substrate consisting of a singleSi, MgO, Al₂O₃, SiO₂, Si₃N₄, or SiC, or a laminated body selected fromSi, MgO, Al₂O₃, SiO₂, Si₃N₄, or SiC.
 4. The laminate substrate accordingto claim 1, wherein the underlying substrate is MgO (111) or a MgO (111)layer is further comprised between the underlying substrate and theintermediate layer.
 5. The laminate substrate according to claim 1,wherein the outermost surface of the intermediate layer is aheteroepitaxially grown Ir (111) film, and the Ir (111) film has acrystallinity wherein a half band width (FWHM) of a diffracted intensitypeak at 2θ=40.7° assigned to Ir (111) analyzed by an X-ray diffractionmethod with a wavelength of λ=1.54 Å is 0.30° or less.
 6. The laminatesubstrate according to claim 1, wherein the intermediate layer has athickness of 5.0 μm or less.
 7. The laminate substrate according toclaim 1, wherein a surface of the metal film of the outermost surface ofthe intermediate layer, which is a film-forming surface of the singlecrystal diamond (111) layer has an off angle within a range, −8.0° ormore and −0.5° or less, or +0.5° or more and +8.0° or less in a crystalaxis [_1_1 2] direction or a threefold symmetry direction thereofrelative to a crystal plane orientation of (111).
 8. The laminatesubstrate according to claim 1, wherein the single crystal diamond (111)layer has a crystallinity wherein a half band width (FWHM) of adiffracted intensity peak at 2θ=43.9° assigned to diamond (111) analyzedby an X-ray diffraction method with a wavelength of λ=1.54 Å is 1° orless, and an FWHM of a rocking curve peak is 4° or less.
 9. The laminatesubstrate according to claim 1, wherein the single crystal diamond (111)layer has, out of impurity concentrations analyzed by SIMS method, anoxygen concentration of 1×10¹⁷ atoms/cm³ or less and a nitrogenconcentration of 5×10¹⁶ atoms/cm³ or less.
 10. The laminate substrateaccording to claim 1, wherein the single crystal diamond (111) layer hasa thickness of 100 μm or more.
 11. The laminate substrate according toclaim 1, wherein the laminate substrate has a diameter of 10 mm or more.12. The laminate substrate according to claim 1, wherein the singlecrystal diamond (111) layer has a surface whose arithmetic averageroughness (Ra) is 2 nm or less.
 13. A freestanding single crystaldiamond (111) substrate, wherein the freestanding substrate has a mainsurface which has an off angle within a range, more than −10.5° and lessthan −2.0°, or more than +2.0° and less than +10.5° in a crystal axis[_1_1 2] direction or a threefold symmetry direction thereof relative toa crystal plane orientation of (111), and the freestanding substrate hasa thickness of 100 μm or more.
 14. A method for manufacturing a laminatesubstrate which includes a single crystal diamond (111) layer,comprising: a step of heteroepitaxially growing an intermediate layer onan underlying substrate whose main surface has an off angle within arange, −8.0° or more and −0.5° or less, or +0.5° or more and +8.0° orless in a crystal axis [_1_1 2] direction or a threefold symmetrydirection thereof relative to a crystal plane orientation of (111), anuclei formation step of forming diamond nuclei on a surface of theintermediate layer, and a step of heteroepitaxially growing, on theintermediate layer surface on which the nuclei are formed, a singlecrystal diamond (111) layer which has an off angle within a range, morethan −10.5° and less than −2.0°, or more than +2.0° and less than +10.5°in a crystal axis [_1_1 2] direction or a threefold symmetry directionthereof relative to a crystal plane orientation of (111).
 15. The methodfor manufacturing a laminate substrate according to claim 14, wherein,in the step of heteroepitaxially growing the intermediate layer, theintermediate layer is a metal film selected from an Ir (111) film, a Rh(111) film, a Pd (111) film, and a Pt (111) film.
 16. The method formanufacturing a laminate substrate according to claim 14, wherein, inthe step of heteroepitaxially growing the single crystal diamond (111)layer, the diamond layer which is heteroepitaxially grown has athickness of 100 μm or more.
 17. The method for manufacturing a laminatesubstrate according to claim 14, wherein, in the step ofheteroepitaxially growing the intermediate layer, a substrate which isMgO (111) crystal at least on an outermost surface is used as theunderlying substrate, and in the step of heteroepitaxially growing theintermediate layer, the intermediate layer is heteroepitaxially grown byan R. F. magnetron sputtering method under conditions: a substratetemperature of 600 to 1200° C. and a pressure of 1.1×10⁻¹ Torr (14.7 Pa)to 9.0×10⁻¹ Torr (120.0 Pa).
 18. A method for manufacturing afreestanding single crystal diamond substrate, wherein a freestandingsingle crystal diamond (111) substrate is obtained by removing at leastthe intermediate layer and the underlying substrate from the laminatesubstrate obtained by the method for manufacturing a laminate substrateaccording to claim 14.